1. Field of the Invention
This invention relates to a reformed vetiver oil or vetiverol, and, more particularly, to a reformed vetiver oil or vetiverol having a smaller isovalencenol content and a greater khusimol content. The invention is also directed to a process for preparing such a reformed vetiver oil or vetiverol and to a perfumery composition containing the same.
2. Description of the Background
Vetiver oils are obtained by the steam-distillation of the roots of Vetiveria zizanoides belonging to the family of Gramineae. The oils are widely used for high-quality, expensive perfumery compositions and soap perfumes. Vetiver oils, however, have a harsh, woody odor inherent to plant roots. Eliminating this odor is essential to obtaining a high-quality perfumery material.
Generally known processes for preparing such perfumery materials are: (1) a process involving the fractional vacuum distillation of vetiver oil; (2) a process involving saponification of vetiver oil, followed by fractional vacuum distillation of the saponified material, and (3) a process comprising reacting vetiver oil and acetic anhydride to convert primary alcohol components into acetates, collecting the acetates by fractional distillation, and saponifying the collected acetate fractions to produce vetiver oil containing primary alcohols as major components. Alcohols contained in the vetiver oil produced by these processes are collectively called vetiverol. Vetiverol gives a warm, sweet, soily, balsamic, lasting fragrance, and is hence used as a high-quality, expensive perfumery material. In particular, the vetiverol produced by the above process (3) has the greatest primary alcohol content among the available vetiverols and is thus considered to be of the highest quality.
This process for producing the highest quality vetiverol, however, is not without some problems. Such problems are exemplified by (1) the difficulty in completely eliminating all alcohol components other than .alpha.-vetivone, .beta.-vetivone, and primary alcohols by the fractional distillation of acetates; (2) the requirement of a rectification step which inevitably subjects the oil to heated conditions for a considerable period of time and tends to cause the oil to be heat-decomposed and deteriorated, producing a tar-like substance, which, in turn, reduces the yield of the target product; and (3) the necessity of expending great effort toward the elimination of an unfavorable, burning smell, and for the improvement of the odor after elimination of such a smell.
The chemical components which impart the fine fragrance of vetiver oils or vetiverols are still to be elucidated. There are very few published reports concerning the means for improving the fragrance of vetiver oils or vetiverols.
In view of this situation, the present inventors have undertaken extensive studies to produce a superior perfumery material from vetiver oils. In the course of this study, the inventors first isolated khusimol and isovalencenol which are the major components of vetiverols to evaluate their fragrance. As a result, the inventors have found that khusimol has a mild, long-lasting, powdery, warm, woody fragrance, and isovalencenol imparts a slightly oily, sandalwood-like fragrance. Furthermore, the inventors discovered that khusimol is a component giving a fragrance inherent to vetiver oils, which cannot be compared to any fragrances produced from any other materials. On the other hand, isovalencenol was found to have an excellent odor itself which is stronger than the odor of khusimol. The odor of isovalencenol, however, was found to act to offset the odor of khusimol inherent to vetiverol. In order to intensify the odor inherent to vetiverol and to further improve its fragrance, it is therefore necessary to selectively reduce the content of isovalencenol and to relatively increase the content of khusimol.
Khusimol and isovalencenol, however, are very similar to each other in their properties, which renders it difficult to separate them from each other using conventionally known refining methods. Only a very small amount can be isolated using gas chromatography, liquid chromatography, column chromatography, rectification, and other known techniques.
The inventors have carried out further studies to develop a process for the separation of khusimol and isovalencenol. As a result, the inventors have found that the primary alcohol components in vetiver oils could be very effectively converted into esters with an acid, especially with a dibasic acid anhydride and that these esters could be separated at a great efficiency to recover the primary alcohols by means of a simple treatment. In addition, the inventors have discovered that although both khusimol and isovalencenol were decomposed by heat or in the presence of a catalyst, the rate of the decomposition of isovalencenol esters was greater than that of khusimol esters, and further that isovalencenol contained in vetiver oils or vetiverols could be selectively decomposed through utilization of this difference of the decomposition rates between the two alcohols. The inventors' discoveries through these studies led to the possibility of eliminating isovalencenol with a high efficiency by a process comprising first esterifying the alcohol components contained in vetiver oils or vetiverols and then subjecting the resulting esters to thermal or catalytic decomposition for the selective removal of isovalencenol esters through the utilization of the difference of the decomposition rate of the two esters. The vetiverols thus prepared with a higher content of khusimol and a lower content of isovalencenol had a mild, elegant odor. Vetiver oils having a higher content of khusimol and a lower content of isovalencenol could produce vetiverols having an excellent odor. These findings have led to the completion of this invention.